Improved method in the manufacture of sodium aluminum sulphate



Patented Sept. 22, 1936 UNITED; STATES IMPROVED METHOD IN THE MANUFACTURE OF SODIUM ALUMINUM SULPHATE Augustus H. Fiske, Warren; and Charles S. Bryan,

Providence, R. L, assignors to Rumford Chemical Works, Rumford, R. I., a corporation of Rhode Island No Drawing. Application March 20, 1935, Serial 11 Claims. (01. 23-118) Our present invention relates to the production of a sodium aluminum sulphate and particularly to one highly suited as an ingredient for food products, such as baking powders or the like.

It is highly desirable that such ingredients be of great purity and free from any discolorations.

Avpure white product therefore has been long sought but has been diflicult to attain commercially on account of the presence of impurities in the bauxite source.

The usual method heretofore of manufacturing sodium aluminum'sulphate has been in general to dissolvea hydrated oxide of aluminum source in sulphuric acid. The usual source was bauxite and while some deposits provide this material in a state of relative purity, it usually contains much extraneous matter. Such impurities in the material turned dark when the bauxite was dissolved in sulphuric acid and tended to persist when the insoluble residue was filtered off. The bauxites used usually contained metallic impurities and these were removed by treating with hyd Ogen sulphide and precipitating and filtering the precipitated sulphides from the solution. The solution was then treated with a solution of sodium sulphate and the combined solutions concentrated to the point where crystallization took place. After crushing and washing, to remove the impure mother liquor, the crystals were heated in a furnace to drive off the water of crystallization, and the resultant sodium aluminum sulphate of commerce while generally satisfactory as to purity was rendered'more costly because of this long process of manufacture.

We have ,devised a process by which the procedure can be very materially shortened without any sacrifice of purity and a product produced which is of a much desired whiteness.

:In accordance with our. invention we reduce a bauxite of a very high grade of purity to a fine powder. This is run into amixer with a calculated amount of so-called salt cake which isa commercial form of a mixture of sodium sulphate and acid sodium sulphate. We find this satisfacl tory although we may use acid sodium sulphate or sodium sulphate but as. the salt cake is commercially available and of a desirable purity, we find it economical to supply the sulphate in this form.

The salt cake is reduced to a finely divided state' Other strengths of sulphuric :acid may beused but we have found this strength to be satisfactory for economical commercial operation. The

acid is thoroughly mixed with the previously mixed powders forming with them a soft cake in the mixer which is readily broken up by the stirring arms. into the acid in the mixer if desired, and this has the advantage of avoiding any tendency to-cake and become hard, but the dry ingredients must be added to the acid graduallyand thoroughly stirred'in. The thorough prer'nixing of the powders before meeting the acid'is highly important.

The reaction gives out heat but this is readily controllable. In this reaction the bauxite and the acid combine theoretically as such indicated reactions must be taken as tenta-o tive because of the preferred-excess of sulphuric.

acid used in our process.

In the furnacing at the temperatures de-' scribed, the reaction involves the distillation of the excess of the sulphuric acid from the entire mass of the material during which the acid sodium sulphate becomes. normal sodium sulphate again and probably the combination between the acid sodiumsulphate and the alumi-. num sulphate produces the sodium aluminum sulphate according to such a reaction as In the foregoing statement we have used the term normal sodium sulphate to distinguish from the acid form of sodium sulphate which is written as NaHSOr. What We term normal sodium sulphate is NazSOi. This might be termedneutral sodium sulphate butin commercial .worksamples The premixedpowders may be stirred of supposedly neutral sodium sulphate often have a slight acidic reaction, although they are practically all NazSO4. We therefore designate our mate'rial' as sodium aluminum sulphate in which the sodium sulphate is of normal character. Our product thereforewill be understood as represented by the formula Na2SO4A12(SO4)a and not NaI-ISOrAMSOQs nor NaHSO4AlHa(SO4)'3 nor;

Na2SO4AlH3 (S04) 3. Y

\ The bleaching action herein referred to goes" ondu'ring this heating or the material in' the fur nace or muflie. It is a combination between the After thoroughly mixing, the material is discharged from the mixer and preferably allowed to stand for a short time to make sure that the sulphuric acid has penetrated all the particles of the mixture and caused a complete chemical combination. We then place this material ina furnace heated above 640 h; which is the boiling point of pure sulphuric acid. As our upper limit we set 1418 F. which must not be exceeded as it represents the decomposition, point. of alu minum sulphate.

' If the material is being handled in large quantities care must be taken not to overheat it. If there develops a. tendency to overheating the temperature of. the furnace should be preferably heldjustbelow a: very dullred heat in which case suckwouldbethe upper limit. This is equivalent toiabout; 9,68? F.- and on commercial scales with large; bodies of material. it is probably the safest working, temperature forour process. The heat- ,ingris carried. on. according to the temperature andthesize of the charge. The mixture of the aluminumsulphate. and the sodium sulphate when heated; and: the water and excess .sulphuric acid driitemofiygives us Al2Na2(SO4)4 which is sodium aluminum sulphate. We have found that a 500 noundpharge can usually be heat treated in about 8 hours at which timeit will be found to be a white lumpy material-which can be ground and otherproducts.

used in the'manufacture of baking powders or days before. furtherprocessing in order to be sureithatsthe reactionsare complete. The. soft cake .soformed..is.then placed in a furnace-to which..may. he attached acondenser to recover the.excess-sulphu1ic acid. which distills from the a materials Attheendofabout 8 hours, according: to the temperatures.employed, the material can be withdrawn from the furnace, cooled and powderedizasbefore explained. 1

:-.We .do=.=notiz.confine. ourselves-exactly to the above. proportions but they are illustratively approximate and. our process works eificiently on suchea. basis. 'Wepreferably use an amount of sulphuricacid. in. excess. of the theoreticalv amount-necessary.- for. ordinary calculated chemicaltreactions. to combine .with the. bauxite as it is.

" our experience that if .we use very. much less than theabove specified amount of sulphuric. acidthe reaction is aptnot to run satisfactorily. More than.the;aboye,amQ lnt of theacidwould, we belie-ye; represent waste- The-excess sulphuric acid. lisifl sn tssi Qrdin r ea tive. u ction has the. bleaching efiect before described andthe result-. at. r uct. m uced is. a. material or. snowy whiteness, The excess. sulphuric acid obtained? from the,v furnaceby; condensationis. preserycdr.

. faint traces of carbon compounds in the material and used as a byproduct for whatever purposes acid of this quality is ordinarily employed.

We find that volatile impurities such as chlorides, fluorides, carbonates, organic matter, arsenic compounds and all impurities volatile at the temperature employed are set free by the sulphuric acid and volatilized by the heat'during the furnacing process.

" As above stated, we find it desirable to premix the. dry ingredientsand stir them into the acid. It is permissible to mix the sodium sulphate (or salt cake) with the sulphuric acid and then add the aluminum oxide (or bauxite) to that mixture.

We-indicate as. undesirable the addition of the aluminum oxide (or;- bauxite) to the sulphuric acid because experience has shown that such a mixture tends to. form a stone-like mass which is impossible to mix, to break up or handle in a satisfactory commercial way as in a mechanical mixer.

Other variations in the steps of the method and. the proportions of: materials as before indicatedmay. beresorted to within theindicated limits 'without departing from thespirit of our invention and will; be readily variedby those skilled; in calculating such proportions according to the materialsused: and .the equipmentavailable.

What we therefore. claim and desireto secure by Letters Patent is:

1-,, Ina methodof. manufacturing sodium aluminum sulphate, those steps consisting in pow-- dering. a. mineral sourcepfcommercially pure hydrated oxide ofaluminum and a sodium'sulphate', in. intimately mixing. the two: powdered materials together in approximately equal pr0portionsbyweight, in. treating the powdered mixture with sulphuric acid inapproximately the ratio of* three parts by weight to one part by weight of the hydrated. oxide of aluminum-orthe sodiumsulphate, and in subjecting. the resultant product to,a sustained heat. treatment between approximately.- 6.40? F}. and: 1418- F. until- 'the entirecharge. has. become substantially pure sodium aluminiunsulphate.

2. In a method of manufacturing'sodium aluminum. sulphate, those-stepsconsisting in powdering a. bauxite. of: high purity and asodiumsulphate, in intimately mixing the two-"powdered materials together in approximately equal proportions, by. weight, in treatingthe powdered mixture with sulphuric acid in approximately theratioof. three partsby weight of sulphuricacid to one. partby. weight ofeither-bauxite or sodium= sulphatev and. in subjecting the. resultant prodnot. to a sustained heat: treatment between approximately 640v F. and.14:18 Fg; until-the entirecharge has become. sodium aluminumsulphate.

3. In a methodof: manufacturing sodium aluminum sulphate,. those steps consisting inipowdering bauxite .of. I high purity and. sodium sul phate, in. intimately; mixing the. two powdered materials together in:v approximately. equal. pro-. portions... by. weight; in. treating. thepowdered mixture with. an. excess of pure... sulphuricacid; in approximately the: ratio of: three. parts: by weight' of sulphuric. .acidto onepart by weight of either bauxite. or. sodium sulphate. and in..sub-;. jecting. the resultant product. to. asustainedrheat. treatment between. approximately..- 6409. F: and: 14.1.8? F. until. the. entire. chargerhas. become.- sodium .aluminum sulphate;

4.. In a method 10f manufacturing sodiumzalue. minum. sulphate,.;thosetsteps consistingyinimixingg atpowderedmineral :sourceof commercially-pure..

hydrated oxide of aluminum with a powdered sodium sulphate in approximately equal proportions by weight, in treating the powdered mixture with an excess of pure sulphuric acid in approximately the ratio of three parts by weight of sulphuric acid to one part by weight of the hydrated oxide of aluminum or the sodium sulphate and in subjecting the resultant product to a sustained heat treatment between approximately 640 F. and 1418" F. until the charge has become a white lumpy substantially pure sodium aluminum sulphate and adapted to be ground to powdered form for compounding in baking powder or like products. 7

5. In a method of manufacturing sodium aluminum sulphate, those steps consisting in mixing a powdered mineral source of commercially pure hydrated oxide of aluminum with a powdered sodium sulphate in approximately equal proportions by weight, in treating the powdered mixture with an excess of pure sulphuric acid in approximately the ratio of three parts by weight of sulphuric acid to one part by weight of the hydrated oxide of aluminum or the sodium sulphate and in subjecting the resultant product to temperatures between 640 F. and 1418 F. until the charge has become a white lumpy substantially pure sodium aluminum sulphate and adapted to be ground to powdered form for compounding in baking powder or like products.

6. In a method of manufacturing sodium aluminum sulphate, those steps consisting in intimately premixing in powdered form a mineral source of commercially pure hydrated oxide of aluminum and a powdered sodium sulphate in approximately equal proportions by weight, in treating the powdered mixture with an excess of pure sulphuric acid in approximately the ratio of three parts by weight of sulphuric acid to one part by weight of the hydrated oxide of aluminum or the sodium sulphate and in subjecting the resultant product to a sustained heat treatment below 1418 F. until the charge has become a white lumpy substantially pure sodium aluminum sulphate and adapted to be ground to powdered form for compounding in baking powder or like products. 7

'7. The process of manufacturing sodium aluminum sulphate consisting first in finely powdering bauxite of high purity and commercial salt cake, next in intimately dry mixing together the powdered bauxite and powdered salt cake in the ratio of approximately 333 pounds of bauxite to 300 pounds of salt cake, next in reacting the 8. The process of manufacturing sodium aluminum sulphate consisting first in finely powdering bauxite of high purity and commercial salt cake, next in ultimately dry mixing together the powdered bauxite and powdered salt cake in the ratio of approximately 333 pounds of bauxite to 300 pounds of salt cake, next in reacting the mixture of bauxite and salt cake with approximately 1000 pounds of sulphuric acid of 66 Baum strength by mechanically mixing the same for approximately twenty minutes to produce a soft cake of material, in letting the product stand for approximately four days to complete reactions, in subjecting the product to a sustained heat treatment between approximately 640 F. and 1418 F. for approximately eight hours until the excess sulphuric acid has been removed and the charge has become a white sodium aluminum sulphate of normal sodium sulphate character.

9. In the production of sodium aluminum sulphate, those steps consisting in simultaneously reacting approximately equal proportions by weight of comminuted hydrated oxide of aluminum and sodium sulphate with approximately three parts by weight of sulphuric acid to every one part of either the hydrated oxide of aluminum or the sodium sulphate, to develop aluminum sulphate and acid sodium sulphate, and in heating to above the boiling point of the acid without decomposing the aluminum sulphate, whereby asodium aluminum sulphate is produced of a normal sodium sulphate character.

10. In the production of sodium aluminum sulphate, those steps consisting in simultaneously reacting approximately equal proportions by weight of an intimate dry mixture of comminuted hydrated oxide of aluminum and sodium sulphate with approximately three parts by weight of sulphuric acid to every one part of either the hydrated oxide of aluminum or the sodium sulphate, to develop aluminum sulphate and acid sodium sulphate and in heating to above the boiling point of the acid without decomposing the aluminum sulphate whereby a sodium aluminum sulphate is produced of a normal sodium sulphate character.

11. In the production of sodium aluminum sulphate, those steps consisting in simultaneously reacting approximately equal proportions by weight of comminuted hydrated oxide of aluminum and sodium sulphate with an excess of approximately three parts by weight of sulphuric acid to every one part of either the hydrated oxide of aluminum or the sodium sulphate, to develop aluminum sulphate and acid sodium sulphate, and in heating to above the boiling point of the acid without decomposing the aluminum sulphate whereby a sodium aluminum sulphate is produced of a normal sodium sulphate character.

AUGUSTUS H. FISKE. CHARLES S. BRYAN. 

